Sand shark
Sand sharks, also known as sand tiger sharks, grey nurse sharks or ragged tooth sharks, are mackerel sharks of the family Odontaspididae. They are found worldwide in temperate and tropical waters. There are three living species are in two genera; Carcharias, and Odontaspis. Many extinct species date back to the Cretaceous, and include such oddities as the filter-feeding Pseudomegachasma. Description The body tends to be brown with dark markings in the upper half. These markings disappear as they mature. Their needle-like teeth are highly adapted for impaling fish, their main prey source. Their teeth are long, narrow, and very sharp with smooth edges, with one and on occasion two smaller cusplets on either side. Sand sharks have a large second dorsal fin. The sand shark can grow up to 3.2 m (10 ft) long, and most adults can weigh around 200 kg (440 lb). The average lifespan of both sexes is only about 7 years, though they may live longer in captivity. Habitat and Name Origins The name sand shark comes from the sharks' tendency toward shoreline habitats, and they are often seen swimming around the ocean floor in the surf zone; at times, they come very close to shore. They are often found in warm or temperate waters throughout the world's oceans, except the eastern Pacific. They also frequent the Mediterranean and Adriatic Seas at depths from 20 to 200 m (66 to 656 ft) and sometimes more. The bigeye sand tiger in particular seems to be exclusively a deep-water hunter, as its large eyes, dark coloration and extremely elusive nature indicate. Behavior The sand shark (Carcharias taurus) has a unique hunting strategy. It is able to gulp air from above the surface and collect the air in its stomach. This enables them to become buoyant and approach their prey virtually motionless. During the day, the sand shark stays mostly inactive, but at night, it becomes active and resumes hunting activities. Their staple is small fish, but will eat crustaceans, squid and smaller sharks as well. They occasionally hunt in groups referred to as shivers, and have even been known to attack full fishing nets in pursuit of easy meals. Smalltooth sand tigers are believed to hunt similarly, but live at greater depths and are predominantly ambush lunge-feeders. Bigeye sand tigers, being rarely seen and poorly known, remain a mystery in their hunting habits, though they are known to eat squid and mesopelagic bony fish. Species Below is a list of species and genera within the sand shark family. Species marked with a "†" are considered extinct: * Family Odontaspididae ** Genus Carcharias *** Carcharias taurus (sand tiger shark) ** Genus ''Odontaspis'' *** Odontaspis ferox (smalltooth sand tiger shark) *** Odontaspis noronhai (bigeye sand tiger) *** Odontaspis actutissima † *** Odontaspis aculeatus † *** Odontaspis acutissima † *** Odontaspis bicarinatus † *** Odontaspis bronni † *** Odontaspis contortidens † *** Odontaspis crassidens † *** Odontaspis cuspidata † *** Odontaspis exilis † *** Odontaspis incurva † *** Odontaspis macrota † *** Odontaspis macrota semistriata † *** Odontaspis malletiana † *** Odontaspis sanguinei † *** Odontaspis speyeri † *** Odontaspis verticalis † *** Odontaspis vorax † *** Odontaspis winkleri † **** Subfamily odontaspinae ***** Genus ''Striatolamia'' † ***** Genus ''Carcharoides'' † ***** Genus ''Parodontaspis'' † ***** Genus ''Priodontaspis'' † ***** Genus ''Pseudoisurus'' † ***** Genus ''Synodontaspis'' † ****** Subfamily ''Johnlonginae'' ******* Genus ''Johnlongia'' † ******* Genus ''Pseudomegachasma'' † Reproduction Sand sharks of all species only develop two embryos, one in each uterus. The largest and strongest embryos consume their siblings in the womb (intrauterine cannibalism) before each surviving pup is born. They have one of the lowest reproduction rates of all sharks and are susceptible to even minimal population pressure, so they are listed as vulnerable and are protected throughout much of their ranges. Interactions With Humans And Recorded Attacks Sand sharks are known to attack humans, though this is extremely rare and nearly unheard of. If a person were to provoke a sand shark, it may retaliate defensively. Sand sharks, particularly those of the genus Carcharias, are generally not aggressive but are known harass divers who are spearfishing. In North America wreck divers regularly visit the World War II shipwrecks to dive with the Sand Tiger sharks that make the wrecks their home and hunting grounds. Sand sharks also were often hunted due to their perceived nature as man-eaters due to their fearsome appearance, though in truth, sand sharks are by no means interested in humans as prey and have neither the interest or the dentition for consuming such large creatures. These sharks are highly popular in captivity in public aquaria due to their large size, fearsome appearance, slow-moving nature and relatively easy care compared to other sharks. They are well-studied as such, and many aspects of shark biology and reproduction have been learned through studying them. However, they are noted for developing spinal problems if kept in insufficiently sized tanks. Conservation A recent report from the PEW Charitable Trusts suggests a new management approach used for large mammals that have suffered population declines could hold promise for sharks. Because of the life-history characteristics of sharks, conventional fisheries management approaches, such as reaching maximum sustainable yield, may not be sufficient to rebuild depleted shark populations. Some of the more stringent approaches used to reverse declines in large mammals may be appropriate for sharks, including prohibitions on the retention of the most vulnerable species and regulation of international trade. Category:Chondrichthyes Category:Elasmobranchs Category:Sharks Category:Odontaspids Category:Lamniformes